The present invention generally relates to fiber optics and specifically to controlled illumination of a cavity by means of a light source and a fiber optics for feeding light from said source into the cavity and having a control means between said light source and the entrance plane of the fiber optics for controlling the luminous density at the exit plane of the fiber optics.
Devices of the type just described are used, among other purposes, in connection with mirror systems or instruments for inspection of cavities. A well known example of such an instrument is the endoscope used in the medical art for direct inspection of body organs or for technological use in the inspection of inaccessible inner spaces of cavities of machines and the like. Preferably, such illuminating devices also include a heat eliminating means, such as a filter arranged between the light source and the entrance of the fiber optics so as to prevent that heat radiation enters into the fiber optics. Consequently, such illuminating devices are sometimes referred to as "cold-light sources."
Various means are known to influence illumination of a cavity by means of the luminous density at the exit end of the fiber optics. For example, the luminous density or light-flux from the light source can be controlled by means of changing the feeding current or voltage of the electric light source or by changing the effective phase section of the feeding current. However, this will change the color temperature of the light source and thus the color of the illuminated object; such color change is particularly disadvantageous if the image of the mirror instrument is to be photographed or transmitted or recorded by video techniques. Further, for illumination control, a neutral or gray wedge, Goldberg wedge, wedge filter or the like absorptive device can be arranged in the optical path between the light source and the entrance of the fiber optics. The range of varying luminous densities by means of a gray wedge is limited, however, and a gray wedge or the like does not permit unobstructed permeation of light but will always reduce maximum illumination of the cavity. Further, a conventional optical diaphragm can be used but this has disadvantages as well. For example, an iris diaphragm will change the entrance angle of the light into the fiber optics and the exit angle of the light emanating from the fiber optices; sectored diaphragms or fan-fading diaphragms have the disadvantage that at least one diaphragm sector will remain in the light path even at maximum aperture and thus will reduce, as does the gray wedge, the maximum illumination of the cavity that would otherwise be possible with the specific light source and light transmission capacity of the system used.